Are there any chaps that I can put in the tank with my goldfish that will keep it clean - but not plecos or snails?

I would have to say no,not really.And even Pleco's and snails have their good and bad.Both of those guys are huge waste producer's,Although they do help with some algae and eating food on the bottom, I really don't count on them to keep it clean.Instead,a great water maintainence schedule,and a weekly gravel vac seems to be a better solution. JMO though. .

isnt good bacteria go away from gravel if you disturb it every week!

^actually, beneficial bacteria will benefit from having the gravel being turned over frequently. It's because BB need oxygen and gravel that's become compacted collects detritus and debris at the bottom and encourages anaerobic bacteria to proliferate.

Good bacteria adheres itself to the gravel,as to the muck/waste/poo under the gravel,well,that is all really bad things-especially when left to build up.It can possibly form bad pockets of toxic gas and harm your fish,or cause your fish to have more probs with bacterial and illness ,etc.

As long as you aren't taking the actual gravel out and cleaning it under the sink faucet,your good bio bugs will be fine through gravel vacs.

Ok, that's cool. I do vacuum the gravel and do decent water changes at least once a week.

But the only thing is, my gravel has this ugly green coating on it now that vacuuming does seem to remove. Any good way to get rid of that?

I think you are talking about green algae. It is difficult to remove but it's good for goldies. It removes nitrate(a little) and serve as food for your gf.